The Moving Picture World (July 1907)

282 THE MOVING PICTURE WORLD. may amount to only the small fraction, of a second, are thus recorded in detail. The motion of the plate through the field in this type of chronophotography is sometimes produced hy mount- ing it in the form of a disc and giving it a motion by rotation about an axis perpendicular to the face of the plate through its center. This is the method pursued by Crehore andJ5quire in their "photo-chronograph," an instrument for the study of the velocity of modern projectiles. In this interesting apparatus the projectile is made to break a succession of circuits by penetrating screens placed in its path at given intervals. A polarized ray of light on its way to the photographic plate passes through carbon bisulphide contained within the core qT a coil traversed by the cur- rent. By an ingenious application of the rotary power of this field upon the plane of polarization of the light ray, the latter is prevented from reaching the plate when- ever the circuit is interrupted. The successive instantaneous exposures on a fixed plate were developed by Marey in Paris, and extensively ap- plied by him to the study of movement, particularly to the motion of men and to the lower animals. Next came the successive instantaneous views on sep- arate plates. The overlapping of the successive images taken on a single fixed plate led, naturally, to the develop ment of apparatus in which each exposure should have a free surface to itself. Muybridge, in his Philadelphia experiments, constructed a very extended and intricate apparatus for this purpose. He used several batteries of cameras for fixed plates with quick moving shutters that could be operated electrically by the experimenter. The result of this work was published in a series of 781 folio plates, each consisting of a group of instantaneous photographs dealing with every type of animal loco- motion. - - . Marey, in France, has devised many instruments for this sort of chronophotography, and among them is an ingenious .form of camera known as the photographic gun. This apparatus was designed particularly for taking chronophotographs of birds in flight and other rapidly moving objects. The lens is in the barrel of the gun, the breech of which contains the sensitive plate, cut into the form of a disk or octagon and mounted so as to revolve rapidly under the action of a spring when released by the trigger. Twelve exposures are made in one second with this instrument by means of a disk shutter, the opening in which gives an exposure of one-seven hundred and twen- tieth of a second. Another disk with twelve windows carries the sensitized plate with a properly interrupted motion, so that the plate is at rest during each exposure and is moved forward to a new position between times. The photographs taken with the gun were very small but they sufficed for the study of the successive positions of the wings of flying birds and for a variety of other similar objects. The greatest type of chronophotography is the succes- sive instantaneous exposures oh a moving film, and it is this type which has attracted the most attention and which in consequence has been most highly developed, and it owes its present perfection to the demand for subjects' for various forms of the" animated picture machine, a device by means of which chronophotographs projected upon a screen may be viewed by many observers simul- taneously. >'.."*; - . Such machine*. are capable of many applications. Demenyy a pupil of Marey, took chronophotographs 0 | the moving lips of a speaker and, making positives faua these, projected them by means of an attachment to the lantern, which he called the photoscope, for the instruc- tion of deaf mutes for the reading of speech. The same method was used by Mach to exhibit the I growth of vegetation, for which purpose he photography a plant daily through its life and then projected the pic tures with sufficient rapidity to blend the effect by per- sistence of vision, and thus the plant was made to grow I through all the phases of growth and to decline within the interval of a few minutes. Although all of these animated picture machines have! received a multitude of names, they may be described ■ J a form of magic lantern for the projection of pictures] upon a screen. The successive pictures follow one another in the fieldl at the rate of about twenty in every second. In most machines the film, or picture ribbon, as it si called, is moved stepwise, the film remaining at rest dttr-f ing the passage of an open sector in a revolving dislij which admits the light to the screen, and being shifted! the proper distance to bring the next picture into the field | during the intervening period of darkness. The usual size of the pictures on these picture ribbons I is 2.5cm.x2cm. This gives about twenty pictures to eachl foot of ribbon and requires one foot of, film for eachl second of time that the exhibition is to last. Picture! ribbons are usually made into lengths of fifty feet, but inl certain instances where a prolonged scene is to be re-l corded the length runs into thousands and often tens of j thousands of feet. In spite of the many names, there are only two type for the production and exhibition of picture ribbons- that in which the motion of the film is continuous. The device generally used to secure a rapid step-wise motion by which the film is brought to rest for a very brief inter- val of time during which the exposure takes place anfl i then moved to the precise distance for the taking'of next picture, without overlapping or loss of space, con- sists of a series of perforations of equi-distance, running] along each edge of the film. To take sharply defined pictures on a constantly mot-l ing film, which is necessary in the second type of mach; .the exposure must be of negligible length as com] with the velocity of the film, which with the rapid moti given in animated pictures is impracticable, or some vice must be employed to prevent the blurring of the pic] • tures. The most successful device of this kind consi in moving the lense with a motion parallel to that of film. The light from the object to the film then trav downward with the same speed as the latter, and is no relative shifting of the image on the sensitive face, and in this.way it is possible to obtain sharp tures, the exposure of which is properly timed by interposition of an adjustable slit. . The camera for accomplishing this contains lenses mounted on a disk and traveling with the linear velocity as the film itself. NOTICE.—If you wish to get yo« copies regularly, leave an ord< with your News Agent, or send $2.00 for one year's subscript* 01